The present invention relates to pumps and in particular to compact piston pumps.
Pumps for medical applications, such as used in oxygen concentrators, generally need to be compact and quiet to operate discreetly in homes and hospitals. It is thus important to properly muffle the working air as well as reduce vibration during operation of the pump.
One problem with conventional pumps is that they can create excessive noise and vibration as the piston(s) are reciprocated, especially if they are improperly balanced. One reason for this in opposed piston pumps is that the pistons may be coupled to the drive shaft by a single retainer or eccentric element between the connecting rods of the piston. Ordinarily, an eccentric element is mounted to the drive shaft and two nibs or bosses extend axially from each side of the eccentric element to mount the pistons to the drive shaft. A moment, or shaking couple, arises as the drive shaft is turn because of the axial spacing between the pistons.
Another problem with conventional pumps is sealing the crankcase and cylinder(s). Improper sealing of the cylinders to the crankcase or the valve head(s) can cause pressurized air to leak to the outside of the pump, which both reduces pumping efficiency and makes noise. Typical sealing arrangements are either prone to leakage or require costly machining operations on the valve plate. Also, many crankcases are made with open necks to allow the pistons to be slid into the crankcase easily during assembly. Typically, the openings in the neck terminate at the cylinders, which have curved exterior surfaces. This makes sealing the crankcase difficult and typically requires separate seals in addition to that sealing the end of the crankcase, thus increasing assembly complexity and creating a potential leak path between the neck seals and the end seal.
Another problem with conventional pumps is that the valve stops can create excessive noise during operation. Typically, thin flapper valves are used to control the intake and exhaust ports of the valve heads. Because of the exhaust port opens under the force of the compressed air, a valve stop is used to support the valve and prevent it from being hyper-extended beyond its elastic range. Usually the stops have undersides that ramp up from the valve plate to support the tip of the valve farther from the valve plate than the neck of the valve. The valves are usually metal and the stops can be metal or plastic, however, in either case the rapid contact between the two surfaces can generate tapping or clicking sounds that are unacceptable in medical applications. Another problem here is that the thin flat flapper valve can succumb to surface attraction between the flapper and the stop and essentially “stick” to the stop and thus remain open.
Yet another problem confronting the design of low-noise pumps is properly muffling the intake and/or exhaust chambers of the valve heads. This can be done by attaching a muffler element to the valve head either direction or via suitable hoses. Another technique is to run the exhaust air into the crankcase on the non-pressure side of the piston head. In this case, if the crankcase is closed and the pistons are in phase, the crankcase will usually be vented through a muffler to avoid generating pulsations in the pump. Even using the later technique, the valve heads are usually exhausted through hoses leading to the crankcase, which is vented through a muffler directly mounted to the crankcase or at the end of a hose.
Accordingly, an improved pump is needed which addresses the aforementioned problems.